The present invention relates generally to nuclear reactors, and more particularly to mitigating acoustic loads in a nuclear reactor.
A reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has a generally cylindrical shape and is closed at both ends, e.g., by a bottom head and a removable top head. A top guide typically is spaced above a core plate within the RPV. A core shroud, or shroud, typically surrounds the core and is supported by a shroud support structure. Particularly, the shroud has a generally cylindrical shape and surrounds both the core plate and the top guide. There is a space or annulus located between the cylindrical reactor pressure vessel and the cylindrically shaped shroud.
Heat is generated within the core and water circulated up through the core is at least partially converted to steam. Steam separators separate the steam and the water. Residual water is removed from the steam by steam dryers located above the core. The de-watered steam exits the RPV through a steam outlet near the vessel top head for flow outside the RPV to drive a turbine.
The flow of steam through the dryers can be unbalanced or mismatched, with much of the steam flow preferentially passing through the top of the dryer vanes. At increased power levels of the reactor, increased steam flow may cause the steam velocity to exceed the breakthrough velocity in local regions of the dryer vanes. The dryer ceases to remove moisture droplets from the steam in those areas where the breakthrough velocity has been exceeded. Wet steam that breaks through, or exits the dryer, then can cause undesirable effects in the rest of the power plant. In addition to the potential for erosion of the metal components, the excess moisture can transport activated particulates from the reactor to the pipes, turbines and heat exchangers which are downstream of the separator which can increase the dose rate in the turbine hall, and make equipment maintenance more difficult.
One of the sources of loading that has destroyed or damaged equipment is acoustic resonance of the fluid inside a standoff pipe, such as a safety relief valve. The safety relieve valve, or valves, with steam flow past their entrances, and the acoustic resonance which naturally occurs, causes acoustic pressures to travel upstream, causing damage to devices, for example, the steam dryers.
Previous attempts to reduce damage to devices such as steam dryers have included predicting or estimating the loading on the steam dryer, and computing the stress on the dryer, and modifying the dryer to decrease the computed stresses.
Another attempt to reduce the damage to equipment such as steam dryers has included a Helmholtz resonator provided on the relief valves. However, the Helmholtz resonator is a large cantilevered bottle-shaped device which is difficult to support in the environment of a nuclear power generating station.
A Herschel-Quincke tube is used to passively cancel acoustic noise at a single frequency. The Herschel-Quincke tube comprises a main pipe and a bypass pipe connecting two points on the main pipe. The two points are separated by a distance equal to the quarter-wavelength of the frequency to be cancelled. The Herschel-Quincke tube operates on the principal that starting from one point, proceeding to the second point, there are two paths, and along those two paths, the sound is cancelled because along one path, a maximum is reached along the wavelength, and along the other path, the opposite of that maximum is reached.